How to test lvalue or rvalue in this case

Question

The code is as following:

struct A
{
   static int k;
   int i;
};
 
int A::k = 10;
 
A func() { A a; return a; }

My question is, how can I tell whether func().k or func().i is an lvalue or not? If both are lvalues/rvalues, how can I test them?

func().k = 0; // compile ok under g++-4.4 and g++-4.6
func().i = 1; // compile ok with g++-4.4, but g++-4.4 gives an error: 
              //"using temporary as lvalue [-fpermissive]"

Answer 1

func().k is an lvalue and func().i is an xvalue.

You can see this for more details: rvalues and temporary objects in the FCD

Althrough, it is not difficult to test whether they are lvalues or rvalues:

#include <iostream>

struct A
{
    static int k;
    int i;
};

int A::k = 10;

A func( ){ A a; return a; }

void f (int & ) { std::cout << "int& " << std::endl; }

int main ()
{
    func().k = 0;  //ok, because func().k is an r
    f(func().k);
    func().i = 1; //compile error: "using temporary as lvalue"
    f(func().i);  //compile error because func().i is an rvalue of type ‘int’
    return 0;
}